Polymerizable polymeric photoinitiators and radiation curable compositions

ABSTRACT

A polymerizable polymeric photoinitiator according to Formula (I): 
     
       
         
         
             
             
         
       
     
     wherein:
         PL represents an n+m+p-functional polymeric core;   n and m independently represent an integer from 1 to 30;   p represents an integer from 0 to 10;   o is 0 or 1;   INI represents a group selected from the group consisting of a benzophenone, a thioxanthone, a carbazole, a anthraquinone, a camphor quinone, an α-hydroxyalkylphenone, an α-aminoalkylphenone, an acylphosphine oxide, a bisacyl phosphine oxide, an acylphosphine sulfide, a phenyl glyoxalate, a benzoin ether, a benzyl ketal, an α-dialkoxyacetophenone, a carbazolyl-O-acyl-oxime, an α-haloarylketone and an α-haloaryl sulfone;   L 3  and L 4  represent a substituted or unsubstituted divalent linking group comprising 1 to 14 carbon atoms;   A represents a radically polymerizable functional group selected from the group consisting of an acrylate, a methacrylate, a styrene, an acryl amide, a methacryl amide, a maleate, a fumarate, an itaconate, an vinyl ether, an allyl ether, an allyl ester, a maleimide, a vinyl nitrile and a vinyl ester; and   R4 represents a substituted or unsubstituted alkyl group.       

     Radiation curable compositions containing the polymerizable polymeric photoinitiator and methods for preparing the polymerizable polymeric photoinitiator are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage Application of PCT/EP2010/050706, filed Jan. 22, 2010. This application claims the benefit of U.S. Provisional Application No. 61/179,019, filed May 18, 2009, which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a new class of polymerizable polymeric photoinitiators, especially suitable for food compliant radiation curable compositions, and methods for preparing the photoinitiators.

2. Description of the Related Art

A free radical photoinitiator initiates the polymerization of monomers when exposed to actinic radiation by the formation of a free radical. Photoinitiators are frequently used in UV-curable compositions, such as UV-curable inkjet inks.

Two types of free radical photoinitiators can be distinguished. A Norrish Type I initiator is an initiator which cleaves after excitation, yielding the initiating radical immediately. A Norrish Type II-initiator is a photoinitiator which is activated by actinic radiation and forms free radicals by hydrogen abstraction from a second compound that becomes the actual initiating free radical. This second compound is called a co-initiator or polymerization synergist.

A photoinitiator can be a monofunctional compound, but can also be a multifunctional compound, i.e. having more than one photoinitiating group. WO 03/033492 (COATES BROTHERS) discloses multifunctional thioxanthone photoinitiators.

When radiation curable compositions are used for food packaging, toys and dental applications, the amount of extractable residues is a critical issue and needs to be minimized. Low molecular weight compounds are usually not completely built into the polymer network and are prone to be readily extracted or to diffuse out of the cured composition. Therefore, it is a continuous concern to design photoinitiators having a reduced tendency to be extracted or to migrate out of the cured composition.

One approach to minimize the extraction of photoinitiators is the use of photoinitiators with a higher molecular weight. However, polymeric initiators have a tendency to lose reactivity. Hence, often considerable amounts of polymeric initiators are required in order to reach the desired curing speed, thereby also increasing the viscosity to an undesirable level for a great number of applications using radiation curable compositions, such as e.g. inkjet printing. To overcome the undesirable viscosity increase of radiation curable compositions, EP 1616921 A (AGFA GRAPHICS) and EP 1674499 A (AGFA GRAPHICS) disclose radiation curable compositions comprising polymeric photoinitiators, comprising a dendritic polymer core. While the use of a dendritic polymer core is advantageous for maintaining a low viscosity of the radiation curable composition, a further improvement in curing speed is desirable, especially in the absence of nitrogen inertisation.

Another approach in solving the extraction problem is the design of a photoinitiator having one or more ethylenically unsaturated polymerizable groups so that it can be copolymerized with the other monomers of the radiation curable composition. Numerous photoinitiators comprising an ethylenically unsaturated polymerizable group have been disclosed in the literature, for use in radiation curable compositions or as a monomer for the preparation of polymeric photoinitiators.

JP 2004-224993 (NIPPON KAYAKY) discloses self-photopolymerization type photopolymerization initiators for reducing its evaporation or sublimation from cured films of radiation curable compositions. Other (meth)acrylated thioxanthones have been disclosed in, for example, CA 2005283 (BASF) and CA 1180486 (CIBA).

(Meth)acrylated benzophenones are disclosed in, for example, US 2006142408 (NATIONAL STARCH) and GB 925117 (DU PONT).

(Meth)acrylated a-hydroxy-ketones are disclosed in, for example, WO 2005/108452 (ASHLAND), WO 97/17378 (COATES BROTHERS) and EP 538553 A (HUGHES AIRCRAFT).

(Meth)acrylated a-amino ketones are disclosed in, for example, WO 96/20919 (CIBA) and CA 2005283 (BASF).

(Meth)acrylated acyl phosphine oxide initiators are disclosed in, for example, WO 2006/056541 (CIBA), WO 2004/103580 (CIBA) and AU 2003205731 (BASF).

(Meth)acrylated benzil dialkyl acetals are disclosed in JP 2005-082679 (DAINIPPON INK).

Often, the synthesis of the target photoinitiators requires the use of (meth)acryloyl chloride. It is commonly known that (meth)acryloyl chloride is highly reactive and limited in stability. It is often contaminated with cyclic dimers (see for example in JP 2002-187868 (DAICEL CHEMICAL) thus requiring distillation prior to use. Combined with the highly toxic nature of (meth)acryloyl chloride, the limited availability on the market and the high cost, synthetic methods using (meth)acryloyl chloride are not well suited for the preparation of (meth)acrylated photoinitiators on an industrial scale.

WO 2009/068590 (AGFA GRAPHICS) discloses an optimized synthetic method for the preparation of acrylated or methacrylated photoinitiators. Though avoiding highly toxic and unstable reagents, an isolation procedure is still required to obtain high purity (meth)acrylated photoinitiators, suitable for food packaging applications, generating additional costs in production and increasing the ecological footprint.

Therefore, there is still a need for photoinitiators, having a significantly reduced tendency to be extracted or migrate out of the cured composition, having a good compatibility with a wide variety of radiation curable compositions and accessible via a simple and cost efficient synthetic procedure having a reduced ecological footprint.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide a new class of polymerizable polymeric photoinitiators accessible via a simple and cost efficient synthetic procedure.

Further preferred embodiments of the present invention provide a radiation curable composition including such a polymerizable polymeric photoinitiator.

Further preferred embodiments of the present invention provide a radiation curable ink and a radiation curable ink jet ink including such a polymerizable photoinitiator.

These and other preferred embodiments of the present invention will become apparent in the detailed description hereinafter.

A surprisingly simple method was found to solve the above cited problems by preparing a polymerizable photoinitiator requiring no isolation, through the reaction of a photoinitiator having at least one hydroxyl group with a specific monomer in the presence of a catalyst. No organic solvents are necessary, thereby avoiding the unecological removal of solvents. This allows e.g. radiation curable inkjet inks lacking organic solvents, which as a consequence exhibit an improved jetting performance in the printer by improved latency and less failing nozzles.

Solubility problems of an isolated polymerizable polymeric photoinitiator in a radiation curable composition can also be avoided by simply removing the catalyst and using the polymerizable polymeric photoinitiator dissolved in the specific monomer as such for addition to a radiation curable composition.

Other preferred embodiments of the invention have been realized with a polymerizable polymeric photoinitiator as defined below.

Further advantages and embodiments of the present invention will become apparent from the following description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS DEFINITIONS

The term “dye”, as used in disclosing the present invention, means a colorant having a solubility of 10 mg/L or more in the medium in which it is applied and under the ambient conditions pertaining.

The term “pigment” is defined in DIN 55943, herein incorporated by reference, as a colorant that is practically insoluble in the application medium under the pertaining ambient conditions, hence having a solubility of less than 10 mg/L therein.

The term “C.I.” is used in disclosing the present application as an abbreviation for Color Index.

The term “alkyl” means all variants possible for each number of carbon atoms in the alkyl group i.e. for three carbon atoms: n-propyl and isopropyl; for four carbon atoms: n-butyl, isobutyl and tertiary-butyl; for five carbon atoms: n-pentyl, 1,1-dimethyl-propyl, 2,2-dimethylpropyl and 2-methyl-butyl etc. Polymerizable Polymeric Photoinitiators

The polymerizable polymeric photoinitiator according to a preferred embodiment of the present invention has a chemical structure according to Formula (I):

wherein:

-   PL represents an n+m+p-functional polymeric core; -   n and m independently represent an integer from 1 to 30; p     represents an integer from 0 to 10;o is 0 or 1; -   INI represents a group selected from the group consisting of     substituted or unsubstituted benzophenone, a substituted or     unsubstituted thioxanthone, a substituted or unsubstituted     carbazole, a substituted or unsubstituted anthraquinone, a camphor     quinone, an α-hydroxyalkylphenone, an α-aminoalkylphenone, an     acylphosphine oxide, a bisacyl phosphine oxide, an acylphosphine     sulfide, a phenyl glyoxalate, a benzoin ether, a benzyl ketal, an     α-dialkoxyacetophenone, a carbazolyl-O-acyl-oxime, an     α-haloarylketone and an α-haloaryl sulfone; L₃ and L₄ represent a     substituted or unsubstituted divalent linking group comprising 1 to     14 carbon atoms; -   A represents a radically polymerizable functional group selected     from the group consisting of an acrylate, a methacrylate, a styrene,     an acryl amide, a methacryl amide, a maleate, a fumarate, an     itaconate, an vinyl ether, an allyl ether, an allyl ester, a     maleimide, a vinyl nitrile and a vinyl ester; and -   R4 represents a substituted or unsubstituted alkyl group.

In a preferred embodiment, PL represents a polyether, a polyester or a polyamide based polymeric core, more preferably a polyether or a polyester based polymeric core, and most preferably a polyether based polymeric core.

In another preferred embodiment, n+m+p represents an integer from 2 to 50, more preferably n+m+p represent an integer from 5 to 40.

In a most preferred embodiment PL represents a star shaped, branched or dendritic polymeric core, preferably a polyether or polyester core, a polyether being particularly preferred. Dendritic polymeric cores include dendrimers, dendrons, dendrigrafts and hyperbranched polymeric cores. Hyperbranched polymeric cores are particularly preferred because of their simple synthesis compared to dendrimers and dendrons. Dendritic polymeric cores have the advantage over linear or branched polymeric cores of the same molecular weight that they do not increase the viscosity of a radiation curable composition as much as linear or branched polymeric cores. This low viscosity behaviour allows their application in low viscous radiation curable compositions such as, for example, radiation curable inkjet inks.

In a further preferred embodiment, A is selected from the group consisting of an acrylate and methacrylate.

In another preferred embodiment, L₄ is selected from the group consisting of a substituted or unsubstituted alkylene group or an aliphatic ether containing group.

In a most preferred embodiment, R4 represents a methyl group.

In a preferred embodiment, the photoinitiating moiety INI is a α-hydroxyalkylphenone group.

In a preferred embodiment, the photoinitiating moiety INI is a substituted benzophenone group or an unsubstituted benzophenone group.

In a preferred embodiment, the photoinitiating moiety INI is a substituted thioxanthone group or an unsubstituted thioxanthone group.

In a preferred embodiment, the photoinitiating moiety INI is a phosphine oxide group.

Typical polymerizable polymeric photoinitiators according to Formula (I) are given by Table 1, without being limited thereto. It is obvious for those skilled in the art that polymeric initiators have a distribution in molecular weight and degree of substitution. For the sake of clarity, the polymeric initiators are illustrated with one specific molecular weight and/or one degree of substitution.

TABLE 1

OLY-1

POLY-2

POLY-3

POLY-4

POLY-5

POLY-6

POLY-7

POLY-8

POLY-9

POLY-10

POLY-11

POLY-12

POLY-13

Methods of Preparation of Polymerizable Polymeric Photoinitiators

For preparing the polymerizable polymeric photoinitiator according to a preferred embodiment of the present invention, at least one monomer according to Formula (II) is used:

wherein

-   R1, R2 and R3 are independently selected from the group consisting     of a hydrogen, an optionally substituted alkyl group and an     optionally substituted aryl group or R1 and R3 represent the     necessary atoms to form a five to eight membered ring; -   L represents an optionally substituted divalent linking group     comprising 1 to 14 carbon atoms; and -   A represents a radically polymerizable group selected from the group     consisting of an acrylate group, a methacrylate group, a styrene     group, an acryl amide group, a methacryl amide group, a maleate     group, a fumarate group, an itaconate group, a vinyl ether group, an     allyl ether group, an allyl ester group, a maleimide group, a vinyl     nitrile group and a vinyl ester group.

In a preferred embodiment, the radically polymerizable group A is selected from the group consisting of an acrylate and a methacrylate, an acrylate being particularly preferred.

In a further preferred embodiment R2 and R3 both represent hydrogen.

In a preferred embodiment R1 represents hydrogen.

In a more preferred embodiment R1, R2 and R3 all represent hydrogen.

In a preferred embodiment, the divalent linking group L is selected from the group consisting of an optionally substituted alkylene group and an aliphatic ether containing group.

A preferred divalent linking group L is —(—CH₂—CH₂—O—)_(n)—CH₂—CH₂— with n being an integer equal to 1, 2, 3, 4, 5 or 6.

A preferred divalent linking group L is —(—CH₂—)_(n)— with n being an integer equal to 1 to 14, more preferably n is equal to 1, 2, 3, 4, 5 or 6.

Preferred monomers according to Formula (II) are given in Table 10, without being limited thereto.

TABLE 10

Ether-1

Ether-2

Ether-3

Ether-4

Ether-5

Ether 6

Ether-7

Ether-8

Ether-9

Ether-10

Ether-11

The most preferred monomer according to Formula (II) is 2-(2-vinyloxyethoxy)ethyl acrylate represented by the compound Ether-1 in the Table 10.

The method of preparing a polymerizable photoinitiator according to a preferred embodiment of the present invention comprises the steps of:

-   a) providing a polymeric photoinitiator comprising at least one     hydroxyl group; -   b) providing a monomer according to Formula (II):

wherein,

-   R1, R2 and R3 are independently selected from the group consisting     of a hydrogen, an alkyl group and an aryl group or R1 and R3     represent the necessary atoms to form a five to eight membered ring; -   A represents a radically polymerizable group selected from the group     consisting of an acrylate group, a methacrylate group, a styrene     group, an acryl amide group, a methacryl amide group, a maleate     group, a fumarate group, an itaconate group, a vinyl ether group, an     allyl ether group, an allyl ester group, a maleimide group, a vinyl     nitrile group and a vinyl ester group; and -   L represents an optionally substituted divalent linking group     comprising 1 to 14 carbon atoms; and -   c) catalyzing the reaction between the monomer and the polymeric     photoinitiator with a catalyst to a polymerizable polymeric     photoinitiator according to Formula (I).

In a preferred embodiment of the method of preparing a polymerizable polymeric photoinitiator, the catalyst is selected from the group consisting of trifluoroacetic acid, trichloroacetic acid, pyridinium tosylate, crosslinked poly(vinylpyridine)hydrochloride, poly(vinylpyridinium)tosylate and sulfonic acid substituted ion exchangers.

In a most preferred embodiment, the reaction is performed in the absence of an organic solvent. The advantage is that organic solvents need not be removed, which is advantageous both for ecological reasons and when manufacturing radiation curable inkjet inks. These organic solvents tend to evaporate at the nozzles of an inkjet print head during a prolonged non-printing time. When restarting the printer, some nozzles appear to be clogged (=failing nozzles). Latency is the time that a print head can be left uncapped and idle before a failing nozzle appears.

Thus a great advantage of the present method for making the polymerizable photoinitiators is that no organic solvent is required but that the monomer according to Formula (II) can be used as the reaction medium. However, it remains possible in the method for preparing a polymerizable polymeric photoinitiator according to the present invention to use one or more organic solvents in the synthesis.

The monomer according to Formula (II) is preferably used not only as reactant but also as reaction medium. The concentration of the monomer according to Formula (II) will be much larger than the concentration of the polymeric photoinitiator comprising at least one hydroxyl group. Preferably the molar ratio of the monomer according to Formula (II) over the photoinitiator comprising at least one hydroxyl group is at least 2, more preferably at least 5 and most preferably at least 10.

It is also possible to add other monomers to the reaction medium, even other monomers according to Formula (II). In the latter, a mixture of different polymerizable polymeric photoinitiators may be obtained depending on the concentration of the different monomers according to Formula (II).

After completion of the reaction, the radiation curable composition includes at least a polymerizable polymeric photoinitiator according to Formula (I), a monomer according to Formula (II) and a catalyst. In a number of cases the catalyst may remain in the radiation curable composition if it does not interfere with the application or the curing of the curable composition. However, most preferably the catalyst is removed. The catalyst could be, for example, polymeric and could lead to an unacceptable viscosity for a UV curable inkjet ink.

The resulting composition including at least one monomer according to Formula (II) capable of free radical polymerization, and a polymerizable photoinitiator, derived from a photoinitiator moiety comprising at least one hydroxyl functional group and the monomer according to Formula (II), can directly be used for the composition of radiation curable compositions, suitable for food packaging applications.

If required for a specific application, the polymerizable polymeric photoinitiator according to Formula (I) can be isolated and purified by any technique known in the prior art such as precipitation, crystallization and optionally chromatography.

Catalysts

Catalysts used for the preparation of asymmetric acetals by addition of an alcohol to alkenyl-ethers, preferably vinyl ethers, include protic acids with a sufficient low pK_(a), such as hydrochloric acid, phosphoric acid, sulfonic acids, sulfuric acid, and carboxylic acids substituted with electron withdrawing groups such as fluorine and chlorine.

Suitable catalysts include organic salts of sulfonic acids, such as pyridine salts. The use of sulfonic acids as catalyst has been disclosed in numerous documents (e.g. Munro et al., Bioorganic and Medicinal chemistry, 16(3), 1279-1286 (2008); Snowden et al. Helvetica Chimica Acta, 89(12), 3071-3086 (2006), Lucatelli et al., Journal of Organic Chemistry, 67(26), 9468-9470 (2002); Wipf et al., Tetrahedron Letters, 40(28), 5139-5142 (1999)) Typical examples are p.-toluene sulfonic acid, 10-camphor sulfonic acid and methane sulfonic acid.

The use of hydrochloric acid has been disclosed in several documents (e.g. Trofimov et al., Tetrahedron Letters, 49, 3104-3107 (2008)). The use of phosphoric acid has been disclosed by Toshiaki et al. (Tetrahedron Letters, 47, 3251-3255 (2006)).

The use of sulfuric acid has been described by Rappe et al. (Justus Liebigs Annalen der Chemie, 601, 84-111 (1956)).

The use of carboxylic acids, substituted with electron withdrawing substituents, has been disclosed in a number of documents (e.g. Rivillo et al., Angewandte Chemie, International Edition, 46(38), 7247-72450 (2007); W02007010483 (Firmenich S;A.); Alvarez de Cienfuego et al., Tetrahedron: asymmetry, 17(2), 1863-1866 (2006); US2005171062 (Allergan Inc.)). Typical examples are trifluoroacetic acid and trichloroacetic acid.

The use organic salts of sulfonic acids has been disclosed in several documents (Lee et al. Bulletin of the Korean Chemical Society, 28(4), 513-514 (2007); Hattori et al., Organic Letters, 10(5), 717-720 (2008); Nakamura et al., Organic Letters, 10(2), 309-312 (2008); Nicolau et al. Journal of the American chemical Society, 129(48), 14850-14851 (2007); Nakamura et al., Tetrahedron, 63(35), 8670-8676 (2007)). A typical example of an organic salt of a sulfonic acid is pyridinium tosylate. Occasionally, also Lewis acids have been reported as catalyst (Alper. H., Synthesis 1972, 81).

Several transition metals have also been shown effective as catalyst for the synthesis of asymmetric acetyls from alkenylethers and alcohols (Maity, G; Synth Commun 1993, 23, 1667; Iqbal, J; Synth Commun 1989, 19, 901; Kantam, M; Synth Commun 1993, 23, 2225; Bhuma, V; Synth Commun 1992, 22, 2941; Ma, S; Tetrahedron Lett 1993, 34, 5269; Molnar, A; Tetrahedron Lett 1996, 37, 8597).

Heterogeneous catalysis has been reported frequently (Bongini, A; Synthesis 1979, 618; Johnston, R; Synthesis 1988, 393; Olah, G; Synthesis 1983, 892; Menger, F; J Org Chem 1981, 46, 5044; Hoyer, S; Synthesis 1986, 655; Upadhya, T; Synth Commun 1996, 26, 4539; Campelo, J; Synth Commun 1994, 24, 1345; Bandgar, B; Synth Commun 1995, 25, 2211; Kumar, P; Synthesis 1993, 1069; Chavez, F; Synth Commun 1992, 22, 159; Patney, H; Synth Commun 1991, 21, 2329; Campelo, J; Synth Commun 1992, 22, 2335).

Acetonyl triphenylphoshonium derivatives have also been reported as catalysts for converting alcohols into asymmetric acetals (Hon et al., Tetrahedron, 57, 5991-6001).

Particularly preferred catalysts are selected from the group consisting of a carboxylic acid substituted with an electron withdrawing group, an organic salt of a sulfonic acid and a heterogeneous catalyst, preferably selected from a salt of crosslinked vinylpyridine containing resins and crosslinked sulfonic acid containing resins.

The most preferred catalysts are selected from the group consisting of trifluoroacetic acid, trichloroacetic acid, pyridinium tosylate, crosslinked poly(vinylpyridine)hydrochloride, poly(vinylpyridinium)tosylate and sulfonic acid substituted ion exchangers.

The acetalysation catalyst can be removed by any technique known in the art. Preferably the catalyst is removed by filtration, neutralization, followed by filtration, neutralization on an ion exchanger or a basic resin and extraction.

Radiation Curable Compositions

The radiation curable composition according to a preferred embodiment of the present invention includes at least the polymerizable photoinitiator according to Formula (I) and most preferably also at least one monomer according to Formula (II). A preferred amount of polymerizable polymeric initiator is 1-50 wt % of the total ink weight, and more preferably 1 to 25 wt% of the total ink weight.

The radiation curable composition preferably contains 2-(2-vinyloxyethoxy)ethyl acrylate as the monomer according to Formula (II).

The radiation curable composition can be used as a colorless liquid or as a colored liquid, in the latter case it is called a radiation curable ink.

In a preferred embodiment, the radiation curable composition according to the present invention is a radiation curable inkjet composition, more preferably a radiation curable inkjet ink.

The radiation curable compositions and inks can also be advantageously used in offset printing, screen printing, flexographic printing and other printing or coating techniques.

The radiation curable compositions and inks are preferably cured by UV radiation.

In a preferred embodiment, the radiation curable composition according to the present invention is substantially free of organic solvent.

The radiation curable compositions and inks are preferably non-aqueous liquids or inks. The term “non-aqueous” refers to a liquid carrier which should contain no water. However sometimes a small amount, generally less than 5 wt % of water based on the total weight of the composition or ink, can be present. This water was not intentionally added but came into the composition via other components as a contamination, such as for example polar organic solvents. Higher amounts of water than 5 wt % tend to make the non-aqueous liquids and inks unstable, preferably the water content is less than 1 wt % based on the total weight of radiation curable composition or ink and most preferably no water at all is present.

The radiation curable compositions and inks preferably do not contain an evaporable component such as an organic solvent. But sometimes it can be advantageous to incorporate a small amount of an organic solvent to improve adhesion to the surface of a substrate after UV-curing. In this case, the added solvent can be any amount in the range that does not cause problems of solvent resistance and VOC, and preferably 0.1-10.0 wt %, and particularly preferably 0.1-5.0 wt %, each based on the total weight of the curable composition or ink.

The radiation curable compositions and inks are preferably part of an ink set, more preferably an inkjet ink set, comprising at least one ink containing one or more colorants, preferably one or more color pigments. The curable ink set preferably comprises at least one yellow curable ink (Y), at least one cyan curable ink (C) and at least one magenta curable ink (M) and preferably also at least one black curable ink (K). The curable CMYK-ink set may also be extended with extra inks such as red, green, blue, and/or orange to further enlarge the color gamut of the image. The CMYK-ink set may also be extended by the combination of full density and light density inks of both color inks and/or black inks to improve the image quality by lowered graininess.

The pigmented radiation curable ink preferably contains a dispersant, more preferably a polymeric dispersant, for dispersing the pigment. The pigmented curable ink may contain a dispersion synergist to improve the dispersion quality and stability of the ink. Preferably, at least the magenta ink contains a dispersion synergist. A mixture of dispersion synergists may be used to further improve dispersion stability.

The viscosity of the curable liquid and ink is preferably smaller than 100 mPa·s at 30° C. and at a shear rate of 100 s⁻¹. The viscosity of the radiation curable inkjet inks and liquids is preferably smaller than 50 mPa·s, more preferably lower than 30 mPa·s, and most preferably between 2 and 15 mPa·s at a shear rate of 100 s⁻¹ and a jetting temperature between 10 and 70° C.

The surface tension of the curable liquid and ink is preferably in the range of about 20 mN/m to about 70 mN/m at 25° C., more preferably in the range of about 22 mN/m to about 40 mN/m at 25° C.

The curable composition or ink may further also contain at least one inhibitor for improving the thermal stability of composition or ink.

The curable composition or ink may further also contain at least one surfactant for obtaining good spreading characteristics on a substrate.

Co-Initiators

The radiation curable composition according to a preferred embodiment of the present invention may contain one or more co-initiators. A preferred amount of the co-initiator is 1 to 30 wt %, more preferably 2 to 20 wt %, and most preferably 5 to 10 wt % of the total weight of the radiation curable composition.

For safety reasons, in particular for food packaging applications, the radiation curable composition according to a preferred embodiment of the present invention contains at least one so-called diffusion hindered co-initiator. A diffusion hindered co-initiator is a co-initiator which exhibits a much lower mobility in a cured layer of the radiation curable composition or ink than a monofunctional, non-polymerizable co-initiator, such as a dialkylaminobenzoate. Several methods can be used to lower the mobility of the co-initiator. One way is to increase the molecular weight of the co-initiator so that the diffusion speed is reduced, e.g. multifunctional co-initiators or polymeric co-initiators. Another way is to increase its reactivity so that it is built into the polymerizing network, e.g. multifunctional co-initiators and polymerizable co-initiators.

The diffusion hindered co-initiator is preferably selected from the group consisting of non-polymeric di- or multifunctional co-initiators, oligomeric or polymeric co-initiators and polymerizable co-initiators. Non-polymeric di- or multifunctional co-initiators usually have a molecular weight between 300 and 900 Dalton. Monofunctional co-initiators with a molecular weight in that range are not diffusion hindered co-initiators.

In a preferred embodiment of the radiation curable composition according to the present invention, the at least one co-initiator is a diffusion hindered dialkylamino substituted aromatic compound selected from the group consisting of an oligomeric or polymeric dialkylamino substituted aromatic compound, a multifunctional dialkylamino substituted aromatic compound and a dialkylamino substituted aromatic compound comprising at least one polymerizable ethylenically unsaturated group. A dialkylamino substituted aromatic compound comprising at least one polymerizable ethylenically unsaturated group is particularly preferred.

In a more preferred embodiment the dialkylamino substituted aromatic compound comprising at least one polymerizable ethylenically unsaturated group is a co-initiator according to Formula (C-I):

wherein,

-   R1 and R2 are independently selected from the group consisting of an     alkyl group, an alkenyl group, an alkynyl group, an aralkyl group,     an alkaryl group, an aryl group and a heteroaryl group; -   R3 to R6 are independently selected from the group consisting of     hydrogen, an alkyl group, an alkenyl group, an alkynyl group, an     acyl group, a thioalkyl group, an alkoxy group, a halogen, an     aralkyl group, an alkaryl group, an aryl group and a heteroaryl     group; -   R7 is selected from the group consisting of hydrogen, an aldehyde     group, a ketone group, an ester group, an amide group, an acyl     group, a thioalkyl group, an alkoxy group, a halogen, a nitrile     group, a sulphonate group, a sulphonamide group, an alkyl group, an     alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group,     an aryl group and a heteroaryl group; R1 and R2, R1 and R3, R2 and     R5, R3 and R4, R4 and R7, R5 and R6, and R6 and R7 may represent the     necessary atoms to form a 5- to 8-membered ring; and with the     proviso that the aromatic amine has at least one α-hydrogen; and -   at least one of R1 to R7 comprises a polymerizable ethylenically     unsaturated functional group selected from the group consisting of     acrylate, substituted acrylate, methacrylate, styrene, acrylamide,     methacrylamide, allyl ester, allyl ether, vinyl ester, vinyl ether,     fumarate, maleate, maleimide and vinyl nitrile. In the polymerizable     co-initiator, preferably R7 represents an electron withdrawing group     selected from the group consisting of an aldehyde, a ketone, an     ester and an amide, and more preferably R3, R4, R5 and R6 all     represent hydrogen.

The alkyl groups, alkenyl groups, alkynyl groups, aralkyl groups, alkaryl groups, aryl groups and heteroaryl groups used for R1 to R7 can be substituted or unsubstituted groups, i.e. a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted alkynyl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkaryl group and a substituted or unsubstituted (hetero)aryl group may be used.

In a preferred embodiment, the polymerizable co-initiator corresponds to Formula (C-II):

wherein,

-   R1 to R6 have the same meaning as defined for Formula (C-I); -   X is selected from the group consisting of 0, S and NR9; -   R8 and R9 are independently selected from the group consisting of     hydrogen, an alkyl group, an alkenyl group, an alkynyl group, -   an aralkyl group, an alkaryl group, an aryl group and a heteroaryl     group; -   R1 and R2, R1 and R3, R2 and R5, R3 and R4, R5 and R6, R4 and R8, R6     and R8, and R8 and R9 may represent the necessary atoms to form a 5-     to 8-membered ring; and at least one of R1 to R6 and R8 comprises a     polymerizable ethylenically unsaturated functional group selected     from the group consisting of acrylate, substituted acrylate,     methacrylate, styrene, acrylamide, methacrylamide, allyl ester,     allyl ether, vinyl ester, vinyl ether, fumarate, maleate, maleimide     and vinyl nitrile. In the polymerizable co-initiator, preferably R3,     R4, R5 and R6 all represent hydrogen.

In one preferred embodiment of the polymerizable co-initiator having Formula (C-II), R1 represents methyl or ethyl and R2 comprises a polymerizable ethylenically unsaturated functional group selected from the group consisting of acrylate, substituted acrylate, methacrylate, styrene, acrylamide, methacrylamide, allyl ester, allyl ether, vinyl ester, vinyl ether, fumarate, maleate, maleimide and vinyl nitrile; and more preferably also R3, R4, R5 and R6 all represent hydrogen.

In another preferred embodiment of the polymerizable co-initiator having Formula (C-I), R1 and R2 independently represent methyl or ethyl and R8 comprises a polymerizable ethylenically unsaturated functional group selected from the group consisting of acrylate, substituted acrylate, methacrylate, styrene, acrylamide, methacrylamide, allyl ester, allyl ether, vinyl ester, vinyl ether, fumarate, maleate, maleimide and vinyl nitrile; and more preferably also R3, R4, R5 and R6 all represent hydrogen.

In a more preferred embodiment, the polymerizable co-initiator corresponds to Formula (C-III):

wherein,

-   R1 and R2 are independently selected from the group consisting of     methyl, ethyl, propyl and butyl; -   L represents a divalent linking group comprising at least one carbon     atom; and -   R10 represents hydrogen, methyl, ethyl, propyl or butyl.

In a preferred embodiment of the polymerizable co-initiator corresponding to Formula (C-III), the divalent linking group L comprises 1 to 30 carbon atoms, more preferably 2 to 10 carbon atoms and most preferably 3 to 6 atoms.

The polymerizable co-initiator may contain two, three or more polymerizable ethylenically unsaturated functional groups independently selected from the group consisting of acrylate, substituted acrylate, methacrylate, styrene, acrylamide, methacrylamide, allyl ester, allyl ether, vinyl ester, vinyl ether, fumarate, maleate, maleimide and vinyl nitrile.

Monomers and Oligomers

The monomers and oligomers used in the radiation curable compositions and inks, especially for food packaging applications, are preferably purified compounds having no or almost no impurities, more particularly no toxic or carcinogenic impurities. The impurities are usually derivative compounds obtained during synthesis of the polymerizable compound. Sometimes, however, some compounds may be added deliberately to pure polymerizable compounds in harmless amounts, for example, polymerization inhibitors or stabilizers.

Any monomer or oligomer capable of free radical polymerization may be used as polymerizable compound. A combination of monomers, oligomers and/or prepolymers may also be used. The monomers, oligomers and/or prepolymers may possess different degrees of functionality, and a mixture including combinations of mono-, di-, tri-and higher functionality monomers, oligomers and/or prepolymers may be used. The viscosity of the radiation curable compositions and inks can be adjusted by varying the ratio between the monomers and oligomers.

Particularly preferred monomers and oligomers are those listed in [0106] to [0115] in EP 1911814 A (AGFA GRAPHICS) incorporated herein as a specific reference.

A preferred class of monomers and oligomers are vinyl ether acrylates such as those described in U.S. Pat. No. 6,310,115 (AGFA), incorporated herein by reference. Particularly preferred compounds are 2-(2-vinyloxyethoxy)ethyl(meth)acrylate, most preferably the compound is 2-(2-vinyloxyethoxy)ethyl acrylate.

Inhibitors

The radiation curable compositions and inks may contain a polymerization inhibitor. Suitable polymerization inhibitors include phenol type antioxidants, hindered amine light stabilizers, phosphor type antioxidants, hydroquinone monomethyl ether commonly used in (meth)acrylate monomers, and hydroquinone, t-butylcatechol, pyrogallol, 2,6-di-tert.butyl-4-methylphenol may also be used.

Suitable commercial inhibitors are, for example, SUMILIZER™ GA-80, SUMILIZER™ GM and SUMILIZER™ GS produced by Sumitomo Chemical Co. Ltd.; GENORAD™ 16, GENORAD™ 18 and GENORAD™ 20 from Rahn AG; IRGASTAB™ UV10 and IRGASTAB™ UV22, TINUVIN™ 460 and CGS20 from Ciba Specialty Chemicals; FLOORSTAB™ UV range (UV-1, UV-2, UV-5 and UV-8) from Kromachem Ltd, ADDITOL™ S range (S100, S110, S120 and S130) from Cytec Surface Specialties.

The inhibitor is preferably a polymerizable inhibitor.

Since excessive addition of these polymerization inhibitors may lower the curing speed, it is preferred that the amount capable of preventing polymerization is determined prior to blending. The amount of a polymerization inhibitor is preferably lower than 5 wt %, more preferably lower than 3 wt % of the total ink or liquid.

Surfactants

The radiation curable compositions and inks may contain a surfactant. The surfactant(s) can be anionic, cationic, non-ionic, or zwitter-ionic and are usually added in a total quantity less than 10 wt % based on the total weight of the radiation curable compositions or ink and particularly in a total less than 5 wt % based on the total weight of the radiation curable composition or ink.

Suitable surfactants include those disclosed in paragraphs [0283] to [0291] of WO 2008/074548 (AGFA GRAPHICS) incorporated herein as a specific reference.

Colorants

Colorants used in the radiation curable inks may be dyes, pigments or a combination thereof. Organic and/or inorganic pigments may be used. The colorant is preferably a pigment or a polymeric dye, most preferably a pigment.

The pigments may be black, white, cyan, magenta, yellow, red, orange, violet, blue, green, brown, mixtures thereof, and the like. This color pigment may be chosen from those disclosed by HERBST, Willy, et al. Industrial Organic Pigments, Production, Properties, Applications. 3rd edition. Wiley-VCH, 2004. ISBN 3527305769.

Suitable pigments are disclosed in paragraphs [0128] to [0138] of WO 2008/074548 (AGFA GRAPHICS).

Suitable pigments include mixed crystals of the above particular preferred pigments. Mixed crystals are also referred to as solid solutions. For example, under certain conditions different quinacridones mix with each other to form solid solutions, which are quite different from both physical mixtures of the compounds and from the compounds themselves. In a solid solution, the molecules of the components enter into the same crystal lattice, usually, but not always, that of one of the components. The x-ray diffraction pattern of the resulting crystalline solid is characteristic of that solid and can be clearly differentiated from the pattern of a physical mixture of the same components in the same proportion. In such physical mixtures, the x-ray pattern of each of the components can be distinguished, and the disappearance of many of these lines is one of the criteria of the formation of solid solutions. A commercially available example is CINQUASIA™ Magenta RT-355-D from Ciba Specialty Chemicals.

Also mixtures of pigments may be used in the radiation curable inks. For some inkjet applications, a neutral black inkjet ink is preferred and can be obtained, for example, by mixing a black pigment and a cyan pigment into the ink. The inkjet application may also require one or more spot colors, for example for packaging inkjet printing or textile inkjet printing. Silver and gold are often desired colors for inkjet poster printing and point-of-sales displays.

Non-organic pigments may be used in the color inkjet inks. Particular preferred pigments are C.I. Pigment Metal 1, 2 and 3. Illustrative examples of the inorganic pigments include red iron oxide (III), cadmium red, ultramarine blue, prussian blue, chromium oxide green, cobalt green, amber, titanium black and synthetic iron black.

Pigment particles in inkjet inks should be sufficiently small to permit free flow of the ink through the inkjet-printing device, especially at the ejecting nozzles. It is also desirable to use small particles for maximum color strength and to slow down sedimentation.

The numeric average pigment particle size is preferably between 0.050 and 1 μm, more preferably between 0.070 and 0.300 μm and particularly preferably between 0.080 and 0.200 μm. Most preferably, the numeric average pigment particle size is no larger than 0.150 μm. An average particle size smaller than 0.050 μm is less desirable for decreased light-fastness, but mainly also because very small pigment particles or individual pigment molecules thereof may still be extracted in food packaging applications. The average particle size of pigment particles is determined with a Brookhaven Instruments Particle Sizer BI90plus based upon the principle of dynamic light scattering. The ink is diluted with ethyl acetate to a pigment concentration of 0.002 wt %. The measurement settings of the BI90plus are: 5 runs at 23° C., angle of 90° , wavelength of 635 nm and graphics=correction function.

However for a white radiation curable ink, the numeric average particle diameter of the white pigment is preferably from 50 to 500 nm, more preferably from 150 to 400 nm, and most preferably from 200 to 350 nm. Sufficient hiding power cannot be obtained when the average diameter is less than 50 nm, and the storage ability and the jet-out suitability of the ink tend to be degraded when the average diameter exceeds 500 nm. The determination of the numeric average particle diameter is best performed by photon correlation spectroscopy at a wavelength of 633 nm with a 4 mW HeNe laser on a diluted sample of the pigmented inkjet ink. A suitable particle size analyzer used was a MALVERN™ nano-S available from Goffin-Meyvis. A sample can be, for example, be prepared by addition of one drop of ink to a cuvet containing 1.5 mL ethyl acetate and mixed until a homogenous sample was obtained. The measured particle size is the average value of 3 consecutive measurements consisting of 6 runs of 20 seconds.

Suitable white pigments are given by Table 2 in [0116] of WO 2008/074548 (AGFA GRAPHICS). The white pigment is preferably a pigment with a refractive index greater than 1.60. The white pigments may be employed singly or in combination. Preferably titanium dioxide is used as pigment with a refractive index greater than 1.60. Suitable titanium dioxide pigments are those disclosed in [0117] and in [0118] of WO 2008/074548 (AGFA GRAPHICS).

The pigments are present in the range of 0.01 to 10% by weight, preferably in the range of 0.1 to 5% by weight, each based on the total weight of radiation curable ink. For white radiation curable inks, the white pigment is preferably present in an amount of 3% to 30% by weight of the ink composition, and more preferably 5% to 25%. An amount of less than 3% by weight cannot achieve sufficient covering power and usually exhibits very poor storage stability and ejection property.

Generally pigments are stabilized in the dispersion medium by dispersing agents, such as polymeric dispersants.

However, the surface of the pigments can be modified to obtain so-called “self-dispersible” or “self-dispersing” pigments, i.e. pigments that are dispersible in the dispersion medium without dispersants.

Dispersants

The dispersant is preferably a polymeric dispersant. Typical polymeric dispersants are copolymers of two monomers but may contain three, four, five or even more monomers. The properties of polymeric dispersants depend on both the nature of the monomers and their distribution in the polymer. Suitable copolymeric dispersants have the following polymer compositions:

-   -   statistically polymerized monomers (e.g. monomers A and     -   B polymerized into ABBAABAB);     -   alternating polymerized monomers (e.g. monomers A and B         polymerized into ABABABAB);     -   gradient (tapered) polymerized monomers (e.g. monomers A and B         polymerized into AAABAABBABBB);     -   block copolymers (e.g. monomers A and B polymerized into         AAAAABBBBBB) wherein the block length of each of the blocks (2,         3, 4, 5 or even more) is important for the dispersion capability         of the polymeric dispersant;     -   graft copolymers (graft copolymers consist of a polymeric         backbone with polymeric side chains attached to the backbone);         and     -   mixed forms of these polymers, e.g. blocky gradient copolymers.

Suitable polymeric dispersants are listed in the section on “Dispersants”, more specifically [0064] to [0070] and

to [0077], in EP 1911814 A (AGFA GRAPHICS) incorporated herein as a specific reference.

The polymeric dispersant has preferably a number average molecular weight Mn between 500 and 30,000, more preferably between 1,500 and 10,000.

The polymeric dispersant has preferably a weight average molecular weight Mw smaller than 100,000, more preferably smaller than 50,000 and most preferably smaller than 30,000.

The polymeric dispersant has preferably a polydispersity PD smaller than 2, more preferably smaller than 1.75 and most preferably smaller than 1.5.

Commercial examples of polymeric dispersants are the following:

-   -   DISPERBYK™ dispersants available from BYK CHEMIE GMBH;     -   SOLSPERSE™ dispersants available from NOVEON;     -   TEGO™ DISPERS™ dispersants from DEGUSSA;     -   EDAPLAN™ dispersants from MUNZING CHEMIE;     -   ETHACRYL™ dispersants from LYONDELL;     -   GANEX™ dispersants from ISP;     -   DISPEX™ and EFKA™ dispersants from CIBA SPECIALTY CHEMICALS INC;     -   DISPONER™ dispersants from DEUCHEM; and     -   JONCRYL™ dispersants from JOHNSON POLYMER.

Particularly preferred polymeric dispersants include SOLSPERSE™ dispersants from NOVEON, EFKA™ dispersants from CIBA SPECIALTY CHEMICALS INC and DISPERBYK™ dispersants from BYK CHEMIE GMBH. Particularly preferred dispersants are SOLSPERSE™ 32000, 35000 and 39000 dispersants from NOVEON.

The polymeric dispersant is preferably used in an amount of 2 to 600 wt %, more preferably 5 to 200 wt % based on the weight of the pigment.

Dispersion synergists

A dispersion synergist usually consists of an anionic part and a cationic part. The anionic part of the dispersion synergist exhibiting a certain molecular similarity with the color pigment and the cationic part of the dispersion synergist consists of one or more protons and/or cations to compensate the charge of the anionic part of the dispersion synergist.

The synergist is preferably added in a smaller amount than the polymeric dispersant(s). The ratio of polymeric dispersant/dispersion synergist depends upon the pigment and should be determined experimentally. Typically the ratio wt % polymeric dispersant/wt % dispersion synergist is selected between 2:1 to 100:1, preferably between 2:1 and 20:1.

Suitable dispersion synergists that are commercially available include SOLSPERSE™ 5000 and SOLSPERSE™ 22000 from NOVEON.

Particular preferred pigments for the magenta ink used are a diketopyrrolo-pyrrole pigment or a quinacridone pigment. Suitable dispersion synergists include those disclosed in EP 1790698 A (AGFA GRAPHICS), EP 1790696 A (AGFA GRAPHICS), WO 2007/060255 (AGFA GRAPHICS) and EP 1790695 A (AGFA GRAPHICS).

In dispersing C.I. Pigment Blue 15:3, the use of a sulfonated Cu-phthalocyanine dispersion synergist, e.g. SOLSPERSE™ 5000 from NOVEON is preferred. Suitable dispersion synergists for yellow inkjet inks include those disclosed in EP 1790697 A (AGFA GRAPHICS).

Preparation of Radiation Curable Inks

The average particle size and distribution is an important feature for inkjet inks. The ink may be prepared by precipitating or milling the pigment in the dispersion medium in the presence of the dispersant.

Mixing apparatuses may include a pressure kneader, an open kneader, a planetary mixer, a dissolver, and a Dalton Universal Mixer. Suitable milling and dispersion apparatuses are a ball mill, a pearl mill, a colloid mill, a high-speed disperser, double rollers, a bead mill, a paint conditioner, and triple rollers. The dispersions may also be prepared using ultrasonic energy.

Many different types of materials may be used as milling media, such as glasses, ceramics, metals, and plastics. In a preferred embodiment, the grinding media can comprise particles, preferably substantially spherical in shape, e.g. beads consisting essentially of a polymeric resin or yttrium stabilized zirconium oxide beads.

In the process of mixing, milling and dispersion, each process is performed with cooling to prevent build up of heat, and for radiation curable inks as much as possible under light conditions in which actinic radiation has been substantially excluded.

The ink may contain more than one pigment, the ink may be prepared using separate dispersions for each pigment, or alternatively several pigments may be mixed and co-milled in preparing the dispersion.

The dispersion process can be carried out in a continuous, batch or semi-batch mode.

The preferred amounts and ratios of the ingredients of the mill grind will vary widely depending upon the specific materials and the intended applications. The contents of the milling mixture comprise the mill grind and the milling media. The mill grind comprises pigment, polymeric dispersant and a liquid carrier. For inkjet inks, the pigment is usually present in the mill grind at 1 to 50 wt %, excluding the milling media. The weight ratio of pigment over polymeric dispersant is 20:1 to 1:2.

The milling time can vary widely and depends upon the pigment, selected mechanical device and residence conditions, the initial and desired final particle size, etc. In a preferred embodiment of the present invention pigment dispersions with an average particle size of less than 100 nm may be prepared.

After milling is completed, the milling media is separated from the milled particulate product (in either a dry or liquid dispersion form) using conventional separation techniques, such as by filtration, sieving through a mesh screen, and the like. Often the sieve is built into the mill, e.g. for a bead mill. The milled pigment concentrate is preferably separated from the milling media by filtration.

In general it is desirable to make the inks in the form of a concentrated mill grind, which is subsequently diluted to the appropriate concentration for use in the printing system. This technique permits preparation of a greater quantity of pigmented ink from the equipment. By dilution, the ink is adjusted to the desired viscosity, surface tension, color, hue, saturation density, and print area coverage for the particular application.

Inkjet Printing Device

Curable compositions and inks according to a preferred embodiment of the present invention may be jetted by one or more print heads ejecting small droplets of ink in a controlled manner through nozzles onto an ink-receiver surface, which is moving relative to the print head(s).

A preferred print head for the inkjet printing system is a piezoelectric head. Piezoelectric inkjet printing is based on the movement of a piezoelectric ceramic transducer when a voltage is applied thereto. The application of a voltage changes the shape of the piezoelectric ceramic transducer in the print head creating a void, which is then filled with ink. When the voltage is again removed, the ceramic expands to its original shape, ejecting a drop of ink from the print head. However the inkjet printing method according to the present invention is not restricted to piezoelectric inkjet printing. Other inkjet print heads can be used and include various types, such as a continuous type and thermal, electrostatic and acoustic drop on demand type.

At high printing speeds, the inks must be ejected readily from the print heads, which puts a number of constraints on the physical properties of the ink, e.g. a low viscosity at the jetting temperature, which may vary from 25° C. to 110° C., a surface energy such that the print head nozzle can form the necessary small droplets, a homogenous ink capable of rapid conversion to a dry printed area, . . . .

The inkjet print head normally scans back and forth in a transversal direction across the moving ink-receiver surface. Often the inkjet print head does not print on the way back. Bi-directional printing is preferred for obtaining a high areal throughput. Another preferred printing method is by a “single pass printing process”, which can be performed by using page wide inkjet print heads or multiple staggered inkjet print heads which cover the entire width of the ink-receiver surface. In a single pass printing process the inkjet print heads usually remain stationary and the ink-receiver surface is transported under the inkjet print heads.

Curing Device

Curable compositions and inks according to a preferred embodiment of the present invention can be cured by exposing them to actinic radiation, preferably by ultraviolet radiation.

In inkjet printing, the curing device may be arranged in combination with the print head of the inkjet printer, travelling therewith so that the curable composition is exposed to curing radiation very shortly after been jetted.

In such an arrangement it can be difficult to provide a small enough radiation source connected to and travelling with the print head. Therefore, a static fixed radiation source may be employed, e.g. a source of curing UV-light, connected to the radiation source by means of flexible radiation conductive device such as a fiber optic bundle or an internally reflective flexible tube.

Alternatively, the actinic radiation may be supplied from a fixed source to the radiation head by an arrangement of mirrors including a mirror upon the radiation head.

The source of radiation arranged not to move with the print head, may also be an elongated radiation source extending transversely across the ink-receiver surface to be cured and adjacent the transverse path of the print head so that the subsequent rows of images formed by the print head are passed, stepwise or continually, beneath that radiation source.

Any ultraviolet light source, as long as part of the emitted light can be absorbed by the photo-initiator or photo-initiator system, may be employed as a radiation source, such as, a high or low pressure mercury lamp, a cold cathode tube, a black light, an ultraviolet LED, an ultraviolet laser, and a flash light. Of these, the preferred source is one exhibiting a relatively long wavelength UV-contribution having a dominant wavelength of 300-400 nm. Specifically, a UV-A light source is preferred due to the reduced light scattering therewith resulting in more efficient interior curing.

UV radiation is generally classed as UV-A, UV-B, and UV-C as follows:

-   -   UV-A: 400 nm to 320 nm     -   UV-B: 320 nm to 290 nm     -   UV-C: 290 nm to 100 nm.

Furthermore, it is possible to cure the image using, consecutively or simultaneously, two light sources of differing wavelength or illuminance. For example, the first UV-source can be selected to be rich in UV-C, in particular in the range of 260 nm-200 nm. The second UV-source can then be rich in UV-A, e.g. a gallium-doped lamp, or a different lamp high in both UV-A and UV-B. The use of two UV-sources has been found to have advantages e.g. a fast curing speed and a high curing degree.

For facilitating curing, the inkjet printer often includes one or more oxygen depletion units. The oxygen depletion units place a blanket of nitrogen or other relatively inert gas (e.g. CO₂), with adjustable position and adjustable inert gas concentration, in order to reduce the oxygen concentration in the curing environment. Residual oxygen levels are usually maintained as low as 200 ppm, but are generally in the range of 200 ppm to 1200 ppm.

EXAMPLES Materials

All materials used in the following examples were readily available from Aldrich Chemical Co. (Belgium) unless otherwise specified. The water used was deionized water.

DPGDA is dipropyleneglycoldiacrylate from SARTOMER.

-   VEEA is 2-(vinylethoxy)ethyl acrylate, a difunctional monomer     available from NIPPON SHOKUBAI, Japan. -   VEEM is 2-(vinyloxyethoxy)ethyl methacrylate, a difunctional monomer     available from NIPPON SHOKUBAI, Japan. -   M600 is dipentaerythritol hexaacrylate and an abbreviation for     MIRAMER™ M600 available from RAHN AG. -   GENOPOL™ TX is an oligomeric thioxanthone available from Rahn AG. -   GENOPOL™ AB is an oligomeric 4-dimethylbenzoic acid derivative     available from Rahn AG. -   Isodecyl acrylate is SR395 available from Sartomer. -   LEWATIT™ M600 MB from BAYER. -   S35000 is an abbreviation used for SOLSPERSE™ 35000, a     polyethyleneimine-polyester hyperdispersant from NOVEON. -   HOSTAPERM™ Blue P-BFS, a cyan pigment (C.I. Pigment Blue 15:4)     available from CLARIANT. -   BYK™-333 is a surfactant available from BYK CHEMIE GMBH. -   PET100 is a 100 μm unsubbed PET substrate with on the backside an     antiblocking layer with antistatic properties available from -   AGFA-GEVAERT as P100C PLAIN/ABAS. -   GENORAD™ 16 is a polymerization inhibitor from RAHN AG. -   DCC is dicyclohexylcarbodiimide. -   DCU is dicyclohexylureum.

COMPINI-1 is a benzophenone type of initiator having the structure:

COMPINI-1 was synthesized as follows:

(4-benzoylphenoxy)-acetic acid was prepared according to Chen et al., Macromolecular Chemistry and Physics (2007), 208(15), 1694-1706. 25.6 g (0.10 mol) (4-benzoylphenoxy)-acetic acid was dissolved in 100 mL toluene and 30 mL dimethyl acetamide. 14.8 g (0.20 mol) sec. butanol and 28 g (0.15 mol) p.-toluene sulfonic acid were added. The reaction mixture was refluxed under azeotropical removal of water. 250 mL ethyl acetate was added and the mixture was extracted with 200 mL 1 N NaOH. The organic fraction was dried over MgSO₄ and the solvent was removed under reduced pressure. COMPINI-1 was isolated as a white crystalline compound. 29.8 g (95%) of COMPINI-1 was isolated.

Type I is an a-alkoxy-ketone Norrish type I initiator having the structure:

This initiator has been prepared according to the following procedure:

80 g (0.36 mol) Darocure 2959, supplied by Ciba Specialty Chemicals, was added to a mixture of 177.05 g (0.95 mol) 2-(vinyloxyethoxy)ethyl acrylate and 80 mL ethyl acetate. 1.6 g BHT (7.1 mmol) and 532 _(})JL (6.9mmol) trifluoro acetic acid were added and the mixture was heated to 70° C. The reaction was allowed to continue for 8 hours at 70° C. Activation of the ion exchanger 1:25 g of Lewatit™ M600 MB was treated with 75 mL of 1 N sodium hydroxide solution and stirred for 2 hours. The ion exchanger was isolated by filtration, washed several times with water and dried until constant weight. The reaction mixture was allowed to cool down to room temperature and 20 g of the activated ion exchanger 1 was added. The mixture was stirred for one hour at room temperature. The ion exchanger was removed by filtration and the ethyl acetate was removed under reduced pressure. The polymerisable Type I initiator was analyzed by ¹H-NMR-analysis and proved to be a 86w% solution in 2-(vinyloxyethoxy)ethyl acrylate. The solution was used as such in the radiation curable compositions.

COINI-1 is a 4-dimethylamino-benzoic acid derivative having the structure:

The synthesis has been disclosed in Example 1 of EP 2033949 A (AGFA GRAPHICS).

COMPINI-2 is Lucirin TPO-L, supplied by BASF:

Type II is a polymerizable thioxanthon having the following structure:

The initiator was prepared according to the following scheme:

Preparation of 2-hydroxy-9H-thioxanthen-9-one

90.8 g (0.59 mol) thiosalicylic acid was dissolved in 840 mL concentrated sulfuric acid. 240 g (2.54 mol) phenol was added and the temperature rose to 75° C. The reaction was allowed to continue for two hours, while slowly cooling down to room temperature. The reaction mixture as slowly added to 1300 mL water at 60° C. The mixture was allowed to cool down to room temperature and the crude 2-hydroxy-9H-thioxanthen-9-one was isolated by filtration. The crude 2-hydroxy-9H-thioxanthen-9-one was suspended in 150 mL ice and 200 mL water. The pH was adjusted to 13.5 using 5N KOH. Upon complete dissolution, the pH was adjusted to 5.4, using acetic acid. 2-hydroxy-9H-thioxanthen-9-one was isolated by filtration and treated with 200 mL water at 75° C. for 30 minutes. 2-hydroxy-9H-thioxanthen-9-one was isolated by filtration washed and dried. 30 g 2-hydroxy-9H-thioxanthen-9-one was isolated.

Preparation of Type II:

28.2 g (0.13 mol) 2-hydroxy-9H-thioxanthen-9-one was suspended in 204.8 g (1.1 mol) 2-(vinyloxyethoxy)ethyl acrylate. 0.5 g BHT was added. The reaction mixture was heated to 70° C. and 0.37 mL (4.8mmol) trifluoro acetic acid was added. The reaction was allowed to continue for 3 hours at 70° C. The reaction mixture was allowed to cool down to room temperature and 35 g of the activated ion exchanger 1 was added. The mixture was stirred for one hour at room temperature. The ion exchanger was removed by filtration and the solution of acrylic acid 2-[2-[1-(9-oxo-9H-thioxanthen-2-yloxy)-ethoxy]-ethoxy]-ethyl ester in VEEA was used as such in the radiation curable compositions.

Measurement Methods 1. Measurement of the ¹H-NMR Spectra

The ¹H-NMR spectra were recorded as follows: a sample of 100 mg of each pre-formulation was dissolved in 0.7 mL CDCl₃. TMS was added as shift reference. The spectra were recorded on a 600 MHz Varian spectrometer (spectral window 10924 Hz (˜18 ppm), acquisition time 5 s, relaxation delay 10s, pulse width 45 deg, number of transients: 32).

2. Curing Degree

The curing degree was tested on a coating immediately after curing with UV light. The cured coating is rubbed with a Q-tip. When the surface is not damaged, the coating is fully cured. When some of the cured coating can be damaged, the coating is only partly cured. When the whole cured coating is damaged, the coating is not cured.

3. Curing Speed

The curing speed on a Fusion DRSE-120 conveyer was defined as the percentage of the maximum output of the lamp needed to cure the samples. The lower the number the higher curing speed. A sample was considered as fully cured at the moment scratching with a Q-tip caused no visual damage.

A percentage of more then 100% of the maximum output of the lamp means that the speed of the conveyer belt had to be reduced to get the sample fully cured at the maximum output of the lamp. The higher the percentage, the more the belt had to be slowed down. A curing speed of 160% means a belt speed of 12.5 m/min at the maximum output of the lamp. A percentage between 150% and 200% is considered as at the edge of practical use. A percentage above 200% is considered out of the range for practical use and no higher percentages are measured.

EXAMPLE 1

This example illustrates the reduced extractability of a polymer according to a preferred embodiment of the present invention.

-   Derivatisation of a polymeric thioxanthone, the synthesis of POLY-7:

GENOPOL™ TX (supplied by Rahn A.G.) was analyzed with ¹H-NMR and HPLC. It was found to be a mixture of compounds. The major components in the mixture proved to have the following structure:

The average degree of esterification was determined using ¹H-NMR. In the supplied batch, 1.5 hydroxyl groups on average were converted into a thioxanthone ester, resulting in 1.5 remaining hydroxyl groups on average. Each degree of esterification showed a distribution in degree of ethoxylation, resulting in a complex mixture of oligomers, having both hydroxyl and thioxanthone end groups.

Preparation of Pre-Formulation 1:

The polymeric initiator was further converted into a polymerizable polymeric photoinitiator, according to the following procedure, resulting in a mixture of polymers, having the following structures as major components:

Pre-treatment of the ion exchanger: 25 g of LEWATIT™ M600 MB was treated with 75 mL of 1 N sodium hydroxide and stirred for 2 hours. The ion exchanger was isolated by filtration, washed several times with water and dried until constant weight.

10 g of GENOPOL™ TX was dissolved in 30 g 2-(2-vinyloxyethoxy)ethyl acrylate. 125 mg trifluoro acetic acid was added and the reaction was allowed to continue for 16 hours at 50° C. The reaction mixture was allowed to cool down to room temperature. 25 g of the pre-treated ion exchanger was added and the mixture was stirred for one hour at room temperature. The ion exchanger was removed by filtration to deliver a Pre-formulation 1.

The mixture was analyzed, using LCMS. 1 mg of pre-formulation 1 was dissolved in 20 mL acetonitrile and analyzed using flow injection LCMS (positive mode, combi ESI-APCI, flow: 0.5 ml/min, operating temperature: 40° C., eluent:MeOH, 10% ammonium acetate, mass range 500-1400). LCMS analysis indicated full conversion of the hydroxyl groups. The Pre-formulation 1 could directly be used for the preparation of radiation curable compositions.

Preparation and Evaluation of Radiation Curable Compositions

A concentrated pigment dispersion Dispersion 1 was made by mixing 466.7 g of a 30 wt % solution of the polymeric dispersant in 535000 in VEEA′ 86.3 g of VEEA, 7.0 g of the stabilizer GENORAD™ 16 and 140.0 g of HOSTAPERM™ Blue P-BFS for 30 minutes using a DISPERLUX™ YELLOW075 (from DISPERLUX S.A.R.L., Luxembourg) and subsequently milling this mixture in a Eiger Lab Bead mill (from EIGER TORRANCE Ltd.) using yttrium-stabilized zirconium oxide-beads of 0.4 mm diameter (“high wear resistant zirconia grinding media” from TOSOH Co.). The bead mill is filled for 52% with the grinding beads and water-cooled during milling at 4250 rpm for 220 minutes. After milling the dispersion was separated from the beads using a filter cloth. The concentrated pigment dispersion Dispersion 1 had an average particles size of 113 nm measured with a MALVERN™ nano-S particle size analyzer and a viscosity of 129 mPa·s at 10 s⁻¹ at 25° C.

The Pre-formulation 1 was directly used for the preparation of the inventive radiation curable compositions.

The extractability of the polymerizable polymeric photoinitiator POLY-7 was compared to the extractability of the starting material GENOPOL™ TX in the same composition. The comparative radiation curable compositions COMP-1 to COMP-5 were prepared according to Table 2. The inventive radiation curable compositions INV-1 to INV-5 were prepared according to Table 3. The weight% (wt %) was based on the total weight of the radiation curable compositions.

TABLE 2 COMP- COMP- COMP- COMP- COMP- wt % of: 1 2 3 4 5 DPGDA 14.40 13.15 10.90 14.40 13.15 M600 16.30 16.30 16.30 16.30 16.30 VEEA 30.00 30.00 30.00 30.00 30.00 GENOPOL ™ TX 4.75 4.75 4.75 1.25 2.50 GENOPOL ™ AB 1.25 2.50 4.75 4.75 4.75 Isodecyl 18.30 18.30 18.30 18.30 18.30 acrylate Dispersion 1 15.00 15.00 15.00 15.00 15.00

TABLE 3 wt % of: INV-1 INV-2 INV-3 INV-4 INV-5 DPGDA 14.40 13.15 10.90 14.40 13.15 M600 16.30 16.30 16.30 16.30 16.30 VEEA 15.75 15.75 15.75 26.25 22.5 Pre-formulation 19.00 19.00 19.00 5.00 10.00 1 GENOPOL ™ AB 1.25 2.50 4.75 4.75 4.75 Isodecyl 18.30 18.30 18.30 18.30 18.30 acrylate Dispersion 1 15.00 15.00 15.00 15.00 15.00

30 mg BYK™-333 was added to each of the comparative and inventive radiation curable compositions.

Coating and Curing of the Radiation Curable Compositions

The free radical curable liquids COMP-1 to COMP-5 and INV-1 to INV-5 were coated on a PET100 substrate using a bar coater and a 10 μm wired bar. Each coated sample was cured using a Fusion DRSE-120 conveyer, equipped with a Fusion VPS/1600 lamp (D-bulb), which transported the samples twice under the UV-lamp on a conveyer belt at a speed of 10 m/min. The samples were cured under nitrogen inerting conditions. Before a coated sample was placed on the conveyer belt, the coated sample was mounted on a metal plate and on top of the plate a metal frame of 1 cm height with a non UV-absorbing quartz glass window was placed, so that a sealed chamber was formed with the coated sample inside. Then, the trapped air in the chamber was replaced by nitrogen gas by introducing pure nitrogen gas into the chamber for 30 seconds. All cured samples were found to be fully cured.

Evaluation of the Amount of Extractable Oligomeric Thioxanthones

Each of the cured samples COMP-1 to COMP-5 and INV-1 to INV-5 were then evaluated on their amount of extractable oligomeric thioxanthones.

Two samples of 7.068 cm² of COMP-1 to 5 and INV-1 to INV-5 were put into a 50 mL beaker and extracted with 4.5 mL acetonitrile, using ultrasound for 30 minutes. The extract was transferred into a 5 mL volumetric flask. The samples were rinsed twice with a small amount of acetonitrile and the rinsing solvent was transferred into the 5 mL volumetric flask until the volume was adjusted to 5 mL. The solution was thoroughly mixed and filtered over a 0.45 mm filter. 10 mL of each sample was injected on the HPLC.

The concentration was determined in comparison with a reference sample of a known concentration of each comparative and inventive initiator, eluted under the same conditions as the extracted samples.

A total coating weight of 10 g/m² was assumed for each sample.

An Alltime C18 5mm column (150 x 3.2 mm), supplied by Alltech, was used. A flow rate of 0.5 mL/min was used at a temperature of 40° C. A DAD detector at 254 nm was used to detect the extracted initiators.

The following HPLC-method was used for all samples.

Eluent A H₂O Eluent B CH₃CN

TABLE 4 Time % eluent % eluent (min) A B 0 55 45 6 55 45 11 0 100 30 0 100 31 55 45 38 55 45

The results are summarized in Table 4. The results are expressed as food ppb. The amount of extractable oligomeric thioxanthone in 14.136 cm², expressed in pg, was determined as described above. This was recalculated to 600 cm², which corresponds to the surface of a 1 litre cube. The recalculated amount of extractable oligomeric thioxanthone corresponds to the maximum amount that can be extracted into one litre of a food stimulant, which is defined as food ppb.

TABLE 5 Extractable oligomeric Radiation curable thioxanthones composition (food ppb) COMP-1 3133 INV-1 594 COMP-2 3127 INV-2 354 COMP-3 561 INV-3 105 COMP-4 1150 INV-4 172 COMP-5 2714 INV-5 380

From Table 5, it becomes apparent that converting the hydroxyl functionalized oligomeric thioxanthone into a polymerizable oligomeric thioxanthone systematically results in a significant reduction of extractable residues.

EXAMPLE 2

This example illustrates the synthesis of the polymerizable polymeric photoinitiators POLY-8 and POLY-11

Synthesis

The polymeric photoinitiators POLY-8 and POLY-11 were prepared according to the following reaction scheme:

Preparation of Intermediate Benzophenone Derivatized Polyglycidol

8 g of a hyperbranched polyglycidol with an average molecular weight 2000, prepared according to W02000/37532 (Bayer A.-G.) and Sunder A. et al, Macromolecules, 32, 4240-4246 (1999), was dissolved in 200 mL dimethyl acetamide at 40° C. 12.9 g (62 mmol) DCC was added and the mixture was stirred for 30 minutes. 13.3 g (52 mmol) 2-(4-benzoylphenoxy)-acetic acid was added and the reaction was allowed to continue for 16 hours at 60° C. The precipitated DCU was removed by filtration and the solvent was evaporated under reduced pressure. The residue was treated with 150 mL dichloromethane and the mixture was cooled to 0° C. After one hour, precipitated DCU was removed by filtration and the solvent was evaporated under reduced pressure. The benzophenone substituted hyperbranched polyglycidol was purified by preparative size exclusion chromatography on a 60×2.5 cm column, PL-gel 10 micron, pore size=500 A, Mw range: 500-30000, supplied by Polymer Laboratories, using tetrahydrofurane, 5% acetic acid as eluent at a flow rate of 10 mL/min and a product load of 200 mg per run. The pooled fractions were evaporated under reduced pressure. The residue was redissolved in 1000mL methylene chloride, extracted with 500 mL brine, dried over MgSO₄ and the solvent was removed under reduced pressure. 6.5 g of the benzophenone substituted polyglycidol was isolated. ¹H-NMR-analysis showed that the isolated polymer was substituted with 7 benzophenone moieties on average.

Synthesis of POLY-8

4.5 g of the benzophenone derivatized hyperbranched polyglycidol was dissolved in 11.5 mL (12 g, 65 mmol) VEEA at 70° C. 18 mg of a 25% divinyl benzene crosslinked polyvinyl pyridine tosylate resin, supplied by Aldrich, was added and the reaction was allowed to continue at 70° C. for four hours and at room temperature for an additional 16 hours. The catalyst was removed by filtration and the solution of POLY-8 in VEEA was used as such in the radiation curable composition of EXAMPLE 3.

Synthesis of POLY-11

2 g of the benzophenone derivatized hyperbranched polyglycidol was dissolved in 5 mL (5.15 g, 26 mmol) VEEM at 70° C. 8.1 mg of a 25% divinyl benzene crosslinked polyvinyl pyridine tosylate resin, supplied by Aldrich, was added and the reaction was allowed to continue at 70° C. for four hours and at room temperature for an additional 16 hours. The catalyst was removed by filtration and the solution of POLY-11 in VEEM was used as such in the radiation curable composition of EXAMPLE 3.

EXAMPLE 3

This example illustrates the advantages in curing speed and extractability of POLY-8 in a radiation curable composition.

Preparation and Evaluation of Radiation Curable Compositions

The comparative radiation curable composition COMP-6 and the inventive radiation curable compositions INV-6 was prepared according to Table 6. The weight% (wt %) was based on the total weight of the radiation curable compositions. Dibutyl phthalate was added to the radiation curable compositions as an internal reference to allow analysis of extractable residues.

TABLE 6 COMP-6 INV-6 COMPINI-1 7.5 — POLY-8 in — 50.0 VEEA Type I 7.5 7.5 COINI-1 7.5 7.5 M600 15.0 15.0 VEEA 60.5 18.0 Dibutyl 2.0 2.0 phthalate

Curing Speed

The free radical curable liquids COMP-6 and INV-6 were coated on a PET100 substrate using a bar coater and a 10 μm wired bar. Each coated sample was cured using a Fusion DRSE-120 conveyer, equipped with a Fusion VPS/1600 lamp (D-bulb), which transported the samples under the UV-lamp on a conveyer belt at a speed of 20 m/min. The curing speed was determined and is shown in Table 7.

TABLE 7 Curing speed Radiation (% of the maximum curable sample output) COMP-6 >400 INV-6 85

From Table 7, it becomes clear that the hyperbranched photoinitiator according to a preferred embodiment of the present invention results in a significant higher curing speed in comparison with a low molecular reference initiator, having the same absorption spectrum.

Extractability of POLY-8

Two samples of 7.068 cm² of INV-6 were put into a 50 mL beaker and extracted with 4.5 mL acetonitrile, using ultrasound for 30 minutes. The extract was transferred into a 5 mL volumetric flask. The samples were rinsed twice with a small amount of acetonitrile and the rinsing solvent was transferred into the 5 mL volumetric flask until the volume was adjusted to 5 ml. The solution was thoroughly mixed and filtered over a 0.45 μm filter. 100 μL of each sample was injected on the GPC.

The concentration was determined in comparison with a reference sample of a known concentration of the initiator, eluted under the same conditions as the extracted samples.

A total coating weight of 10 g/m² was assumed for each sample.

A 3*mixed B column set was used, calibrated with polystyrene standards. THF/5% acetic acid was used as eluent. A RI-detector was used. The flow rate was 1.5 ml/min and the samples were eluted at 40° C.

In the GPC trace no residue of POLY-8 was detectable. This illustrates that a hyperbranched photoinitiator according to a preferred embodiment of the present invention is completely built in into the network.

EXAMPLE 4

This example illustrates the synthesis of the polymerizable polymeric photoinitiators POLY-12 and POLY-13.

Synthesis of POLY-12 and POLY-13

The polymerizable polymeric photoinitiators POLY-12 and POLY-13 were prepared according to the following scheme:

Phenyl(2,4,6-trimethylbenzoyl)phosphinic chloride was prepared according to DE10206117 (BASF A.-G.).

6.5 g of a hyperbranched polyglycidol with an average molecular weight 2000, prepared according to W02000/37532 (Bayer A.-G.) and Sunder A. et al, Macromolecules, 32, 4240-4246 (1999), was dissolved in 160 mL dimethyl acetamide at 50° C. 7.2 mL (5.22 g, 52 mmol) triethyl amine and 14.5 g (43 mmol) phenyl(2,4,6-trimethylbenzoyl)phosphinic chloride were added. The reaction was allowed to continue at room temperature for 16 hours. The precipitated salts were removed by filtration and the solvent was evaporated under reduced pressure. The crude acyl phosphine oxide substituted hyperbranched polyglycidol was purified by preparative size exclusion chromatography on a 60×2.5 cm column, PL-gel 10 micron, pore size=500 A, Mw range: 500-30000, supplied by Polymer Laboratories, using tetrahydrofurane, 5% acetic acid as eluent at a flow rate of 10 mL/min and a product load of 200 mg per run. The pooled fractions were evaporated under reduced pressure. The residue was redissolved in a minimum ethyl acetate and precipitated with hexane. The oily polymeric fraction was isolated and dried under reduced pressure.

Synthesis of POLY-12

3.6 g of the acyl phosphine oxide substituted hyperbranched polyglycidol was dissolved in 50 mL methylene chloride. 9 mL VEEA, 0.3 g BHT and 1 g of a 25% divinyl benzene crosslinked polyvinyl pyridine tosylate resin, supplied by Aldrich, were added and the reaction was allowed to continue for 16 hours at room temperature. The crosslinked polyvinyl pyridine tosylate resin was removed by filtration and the solvent was evaporated under reduced pressure. 11.5 g of a solution of POLY-12 in VEEA was isolated. The solution was used as such in the radiation curable compositions.

Synthesis of POLY-13

3 g of the acyl phosphine oxide substituted hyperbranched polyglycidol was dissolved in 50 mL methylene chloride at 40° C. 7.7 mL VEEM, 0.3 g BHT and 1 g of a 25% divinyl benzene crosslinked polyvinyl pyridine tosylate resin, supplied by Aldrich, were added and the reaction was allowed to continue for 16 hours at room temperature. The crosslinked polyvinyl pyridine tosylate resin was removed by filtration and the solvent was evaporated under reduced pressure. 11.2 g of a solution of POLY-13 in VEEM was isolated. The solution was used as such in the radiation curable compositions.

EXAMPLE 5

This example illustrates the advantages of POLY-12 and POLY-13 in a radiation curable composition.

Preparation and Evaluation of Radiation Curable Compositions

The comparative radiation curable composition COMP-7 and the inventive radiation curable compositions INV-7 and INV-8 were prepared according to Table 8. The weight% (wt %) was based on the total weight of the radiation curable compositions. Dibutyl phthalate was added to the radiation curable compositions as an internal reference to allow analysis of extractable residues.

TABLE 8 wt % of: COMP-7 INV-7 INV-8 COMPINI-2 7.5 — — POLY-12 in — 40.0 — VEEA POLY-13 in — — 40.0 VEEM Type II 7.5 7.5 7.5 COINI-1 7.5 7.5 7.5 M600 15.0 15.0 15.0 VEEA 60.5 28 28 Dibutyl 2.0 2.0 2.0 phthalate

Curing Speed

The free radical curable liquids COMP-7, INV-7 and INV-8 were coated on a PET100 substrate using a bar coater and a 10 μm wired bar. Each coated sample was cured using a Fusion DRSE-120 conveyer, equipped with a Fusion VPS/1600 lamp (D-bulb), which transported the samples under the UV-lamp on a conveyer belt at a speed of 20 m/min. The curing speed was determined and is shown in Table 9.

TABLE 9 Radiation Curing speed Curable (% of the maximum Composition output) COMP-7 60 INV-7 50 INV-8 95

From Table 9, it becomes apparent that the hyperbranched photoinitiators according to a preferred embodiment of the present invention have a good to excellent curing speed.

Extractability of POLY-12 and POLY-13

Two samples of 7.068 cm² of INV-7 and INV-8 were put into a 50 mL beaker and extracted with 4.5 mL acetonitrile, using ultrasound for 30 minutes. The extract was transferred into a 5 mL volumetric flask. The samples were rinsed twice with a small amount of acetonitrile and the rinsing solvent was transferred into the 5 mL volumetric flask until the volume was adjusted to 5 ml. The solution was thoroughly mixed and filtered over a 0.45 μm filter. 100 μL of each sample was injected on the GPC.

The concentration was determined in comparison with a reference sample of a known concentration of the initiator, eluted under the same conditions as the extracted samples.

A total coating weight of 10 g/m² was assumed for each sample.

A 3*mixed B column set was used, calibrated with polystyrene standards. THF/5% acetic acid was used as eluent. A RI-detector was used. The flow rate was 1.5 ml/min and the samples were eluted at 40° C.

In the GPC trace no residue of POLY-12 and POLY-13 was detectable. This illustrates that hyperbranched photoinitiators according to a preferred embodiment of the present invention are completely built in into the network.

While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims. 

1-13. (canceled)
 14. A polymerizable polymeric photoinitiator according to Formula

wherein: PL represents an n+m+p-functional polymeric core; n and m independently represent an integer from 1 to 30; p represents an integer from 0 to 10; o is 0 or 1; INI represents a group selected from the group consisting of a benzophenone, a thioxanthone, a carbazole, a anthraquinone, a camphor quinone, an α-hydroxyalkylphenone, an α-aminoalkylphenone, an acylphosphine oxide, a bisacyl phosphine oxide, an acylphosphine sulfide, a phenyl glyoxalate, a benzoin ether, a benzyl ketal, an α-dialkoxyacetophenone, a carbazolyl-O-acyl-oxime, an αm-haloarylketone, and an α-haloaryl sulfone; L₃ and L₄ represent a substituted or unsubstituted divalent linking group comprising 1 to 14 carbon atoms; A represents a radically polymerizable functional group selected from the group consisting of an acrylate, a methacrylate, a styrene, an acryl amide, a methacryl amide, a maleate, a fumarate, an itaconate, an vinyl ether, an allyl ether, an allyl ester, a maleimide, a vinyl nitrile, and a vinyl ester; and R4 represents an alkyl group.
 15. The polymerizable polymeric photoinitiator according to claim 14, wherein PL represents a polyether, a polyester, or a polyamide based polymeric core.
 16. The polymerizable polymeric photoinitiator according to claim 15, wherein n+m+p represents an integer from 2 to
 50. 17. The polymerizable polymeric photoinitiator according to claim 14, wherein PL represents a star shaped, branched, or dendritic polymeric core.
 18. The polymerizable polymeric photoinitiator according to claim 14, wherein L₄ is selected from the group consisting of an alkylene group and an aliphatic ether containing group.
 19. The polymerizable polymeric photoinitiator according to claim 14, wherein R4 represents a methyl group.
 20. A radiation curable composition comprising: the polymerizable polymeric photoinitiator according to claim
 14. 21. A radiation curable inkjet ink comprising: the polymerizable polymeric photoinitiator according to claim
 14. 22. A radiation curable composition comprising: the polymerizable polymeric photoinitiator according to claim
 14. 23. A radiation curable inkjet ink comprising: 2-(2-vinyloxyethoxy)ethyl acrylate; and the polymerizable polymeric photoinitiator according to claim
 14. 24. A radiation curable composition comprising: the polymerizable polymeric photoinitiator according to claim 14, which is substantially free of organic solvent.
 25. A radiation curable inkjet ink comprising: the polymerizable polymeric photoinitiator according to claim 14, which is substantially free of organic solvent.
 26. A radiation curable inkjet ink comprising: 2-(2-vinyloxyethoxy)ethyl acrylate; and the polymerizable polymeric photoinitiator according to claim 14, which is substantially free of organic solvent.
 27. A method of preparing a polymerizable photoinitiator comprising the steps of: a) providing a polymeric photoinitiator comprising at least one hydroxyl group; b) providing a monomer according to Formula (II):

wherein R1, R2, and R3 are independently selected from the group consisting of a hydrogen, an alkyl group, and an aryl group, or R1 and R3 represent the necessary atoms to form a five to eight membered ring; A represents a radically polymerizable group selected from the group consisting of an acrylate group, a methacrylate group, a styrene group, an acryl amide group, a methacryl amide group, a maleate group, a fumarate group, an itaconate group, a vinyl ether group, an allyl ether group, an allyl ester group, a maleimide, a vinyl nitrile, and a vinyl ester group; and L represents an optionally substituted divalent linking group comprising 1 to 14 carbon atoms; and c) catalyzing a reaction between the monomer and the polymeric photoinitiator with a catalyst to a polymerizable polymeric photoinitiator according to Formula (I) defined by claim
 14. 28. The method according to claim 27, wherein the catalyst is selected from the group consisting of trifluoroacetic acid, trichloroacetic acid, pyridinium tosylate, crosslinked poly(vinylpyridine)hydrochloride, poly(vinylpyridinium)tosylate, and sulfonic acid substituted ion exchangers.
 29. The method according to claim 27, wherein the reaction is performed in the absence of an organic solvent.
 30. The method according to claim 28, wherein the reaction is performed in the absence of an organic solvent. 